Pyrolysis of coal



March 26, 1968 R. T. EDDINGER ETAL PYROLYS I S OF COAL Filed Jan. El,1965 TYPICAL FLOW SHEET 2 Sheets-Sheet 1 FIG. I.

HIGH VOLATILE B BITUMINOUS COAL COAL CRUSH ED FOR FLUIDIZATION OVERHEADTO CONDENSER STAGE l-FLUIDIZED BED DRYING AND PREHEATING HOT FLUE GAS OROTHER INERT GAS OVERHEAD TO CONDENSER STAGE 2- FLUIDIZED BED FIRSTPYROLYSIS soc-900w 24-25% TOTAL OILY LIQUID l0 -3o% TOTAL sAs' OVERHEADTO FLUIDIZE AND HEAT STAGE 2 STAGE 3-FLUlDlZED BED SECOND PYROLYSISOVERHEAD TO FLUIDIZE AND 7 HEAT STAGE 3 STAGE 4- FLUIDIZED BED AND HEATDEVELOPMENT l5OO|8OOF CALCINATION,PARTIAL GASIFICATION AIR OR OXYGENTOFLUIDIZE CHAR 35 T0 60% INVENTORS RALPH TRACY EDDINGER JOHN F. JONESBY LEONARD SEGLIN m 2." PM

March 26, 1968 R. T. EDDINGER ETAL PYROLYSIS OF COAL Filed Jan. 21!,1965 TYPICAL FLOW SHEET 2 Sheets-Sheet HIGH VOLATILE A BITUMINOUS COALCOAL CRUSHED FOR FLUID I ZATION OVERHEAD TO CONDENSER ITO IO/ OFDRYWEIGHT I FLUE GAS CHAR PARTS 1 PART OVERHEAD TO CONDENSER STAGE2-FLUIDIZED BED FIRST PYROLYSIS.

25 32 TOTAL LIQUID IO -30 TOTAL GAS OVERHEAD TO FLUIDIZE STAGE 3-FLUIDIZED BED sEco D PYROLYSIS OVERHEAD TO FLUIDIZE RECYCLE STAGE 4-FLUIDIZED BED THIRD PYROLYSIS 95o- |oso F OVERHEAD T0 HEAT AND FLUIDIZESTAGE 5 FLUIDIZED BED CALCI N ATION, PARTIAL GASI FICATION AND HEATDEVELOPMENT AIR OR OXYGEN CHAR 30 TO 55 INVENTORS RALPH TRACY EDDINGERJOHN F. JONES LEONARD SEGLIN a, Add W2. PM

United States Patent 3,375,175 PYROLYSIS 0F COAL Ralph Tracy Eddinger,Princeton Junction, and John F. Jones, Princeton, N.J., and LeonardSeglin, New York, N.Y., assignors t0 FMC Corporation, New York, N.Y., acorporation of Delaware Filed Jan. 21, 1965, Ser. No. 426,812 8 Claims.(Cl. 201-31) ABSTRACT OF THE DISCLOSURE Increased yield of oils and tarsare obtained from the pyrolysis of coal by conducting the pyrolysis inat least three fluidized stages, the first being carried out underoxygen free conditions below the fusion temperature of the coal bysufliciently high temperature to remove about 140% volatiles from thedry coal, conducting the. so treated coal to at least a second stage toremove nearly all the volatiles from the coal, and to a final stage tosubstantially devolatilize the coal, and recovering the condensablesfrom the overheads of the stages.

This invention resulted from work done under Contract 14-01-0001-235with the Oflice of Coal Research in the Department of the Interior,entered into pursuant to the Act establishing the Oflice of CoalResearch, 30 U.S.C. 661 668.

This invention is concerned with the pyrolysis of coal, and itsprincipal aim is to provide a process for pyrolysis of coal which willinsure the production of maximum amounts of liquid hydrocarbonaceousproducts from the coal.

The economics of coal production is very largely related to. geography,other things being equal. Coal that can be mined cheaply is valuable ornot, depending on whether it or its. conversion products can be readilytransported to points. where. it. can be used. As a result, there arehuge deposits of coal which are capable of inexpensive mining which haverelatively little commercial. value, because they are remote from thepoint of usage; whereas liquid fuels such. as petroleum, because thesecan be transported by pipeline to refineries or ports and cheaplytransferred to tankers. for economic transportation to the using point,are not so limited by geography.

One obvious way of converting coal at the mine to a form in which it isreadily transportable is to build a power plant at the mine andtransport the electrical energy produced therefrom to markets bytransmission lines. Unfortunately, in some areas. where coal isavailable there is no water available for such a plant. Moreover, somedeposits are in areas Where hydroelectric power is abundant, so there.is little economic. incentive to utilize the coal in this fashion.

Another and more flexible approach would be the. provision of somesimple process for converting the coal either to liquid or a combinationof liquid, combustible gas, and solid in. such proportion that theliquid would be in a high enough proportion to the solid to transport itas a slurry in a pipeline.

Even the partial. realization of this possibility will require veryconsiderable increases in the yields of oily ice liquids over knownmethods of low pressure pyrolysis of coal. Experimental methods areknown which yield as much as 20% of the weight of the coal ascondensable liquid; the known commercial methods only yield about 10%.Hydrogenation at high pressures (above about 500 p.s.i.g.) can be usedto increase the yield, but is too expensive.

Ideally the yield of liquid hydrocarbons should approximate at least theyield of residual coke. However, any increase in liquid yields is ofconsiderable value since it reduces the amount of residual char whichcannot be transported by pipeline along with the oil which is moved withit Moreover, it has been noted that as the yields of oil from a coal areincreased, the percentages of polynuclear aromatics are reduced, so thatthe oils from the coal should become more useful as a possible feedstock for the manufacture of products competitive with those obtainedfrom petroleum. This is not surprising since it is believed thatpetroleum and coal merely represent two different products resultingfrom the fossilization of organic matter.

The instant invention has as its principal object the provision of aprocess for pyrolyzing various ranks of coals, and particularly variousbituminous and subbituminous coals to produce maximum yields of liquidsvis-a-vis the solid residues. The method as applied to bituminous coalhas produced maximum yields of about 24% to 25% for high volatile Bbituminous coals and yields of 25% to 32% for high volatile A bituminouscoals.

According to the present invention, we heat finely divided coal in aseries of at least three fluidized beds to progressively highertemperatures under conditions which maximize the yield of liquids. Inthe first stage the finely divided, preferably dry coal, is introducedinto a fluidized bed maintained at a temperature just below thetemperature at which fusion of the mass sufiicient to defluidize the bedwould occur, for a short residence time sufficient to reduce the weightof the moisture-free coal about 1% to about 10%, in the absence of addedoxygen. The overhead from this stage is sent to a condenser whereliquids are condensed out. This removal of volatiles raises the fusiontemperature of the residue, which can thus be overflowed into a secondfluidized bed at a higher temperature, where more of the volatiles canbe removed in the absence of added oxygen, and this, in turn, be passedinto a. further stage(s) where the remainder of the volatiles can beremoved. Oxygen should be omitted in all but the very last stages of theprocess, until after about all of the condensables have been removed.Pressures are low, from atmospheric up to about 500 p.s.i.g.

It is essential to the successful operation of this process that thefiuidizing gas passing through the first stage of the process be free ofvapors from the following stages. This is because this stage of theprocess is the most delicate, and the condensation of the oily materialfrom the vapors from the later stages would cause a lowering'of thefusion point of the mass and consequent loss of'fiuidization.

In the later stages of the process the vapors from succeeding stages canbe passed through. the previous stages to insure better heat utilizationand all of the overheads can be recovered, preferably after being.combined with the overhead from the first stage.

The number of stages needed for any coal to avoid loss of fiuidizationin any stage is dependent on the amount of volatiles in the coal and thetendency of the coal to fuse. Thus a typical Illinois No. 6 Seam coal,which is classified as a high volatile B bituminous coal, can besuccessfully procesesd in 4 stages, while a Pittsburgh Seam coal, whichis classified as a high volatile A bituminous coal, will require 6 to 8stages.

The number of stages needed for any coal can be substantially lowered byrecycling char at a relatively low ratio of recycle to process coal (ofthe order of 2 to 1, to 3 to 1) to the second and subsequent stages.Recycle to the first stage is unnecessary to prevent agglomeration, andis undesirable because of problems in bringing very hot recycle charinto contact with fresh coal. Recycling will, for example, reduce thenumber of stages needed for a high volatile B bituminous coal from 4 to3 and make it possible to process a high volatile A bituminous eoal inas little as stages.

The temperatures used in the various stages depend, of course, on thenature of the coal, and particularly on its fusion point. In general adry high volatile bituminous coal will fuse up in a fluidized bed atabout 630 F. to 700 F., so that a temperature of 600 F. to 650 F.depending on the particular coal involved leaves an adequate margin ofsafety, while being high enough to start the evolution of oil formingvapors which is essential in this stage to permit transfer of the coalto the next higher stage. Low volatile bituminous coals can be heated upto 800 F., whereas high oxygen subbituminous coals can be heated as highas 850 F. in this first stage. Such low volatile coals cannot producehigh yields of liquids, although our process does increase the oilyields over k n-own processes.

It is most surprising that the removal of relatively small amounts ofvolatiles-of the order of as low as 1% to l0%permits the next stage ofthe process to be run at :a temperature as much as 200 F. higher thanthe temperature in the first stage.

Heretofore it has been considered necessary to oxidize the coal in thisstage, in order to permit the use of substantially higher temperaturesin the next stage. This is most undesirable for the production of highyields of oily liquids, since oxidation not only prevents oily liquidfrom being recovered overhead in this first stage, but markedly reducesthe yield in subsequent stages. The removal of small amounts ofvolatiles in the first stage accomplishes the same purpose as oxidation,but apparently by an entirely different mechanism. It seems likely thatthe lowest molecular weight, and hence the lowest melting of thevolatiles in the coal, are driven off first, so that a substantialincrease in fusion temperature is obtained with a very small weightloss, so that substantial increases in temperature can be made in thesucceeding stage, especially with high volatile B bituminous coals.

This is less so in the case of high volatile A bituminous coals, whichapparently contain higher percentages of low molecular weight material.With such coals it is necessa'ry-to proceed more cautiously, even withchar recycle.

Use of oxygen in the intermediate stages, as in the first stage, willreduce oil yields. Apparently the hydrogen in the coal hydrocarbonmatrix, which is essential for the oil production, is oxidized at asomewhat faster rate than carbon. Hence, internal heating by addingoxygen to the fiuidizing gas should be reserved for the final stage, inwhich the feed contains very little volatiles recoverable as oil.

The process can be best understood by reference to the accompanyingdrawings, in which:

FIG. 1 is a flow sheet of our process as applied to one high volatile Bbituminous coal, without char recycle.

FIG. 2 is a flow sheet of our process as applied to one high volatile Abituminous coal, with char recycle.

Referring to the drawings, FIGURE 1 discloses the preferred mode ofoperation with high volatile B bitumi- 4 nous co als. The coal is firstcrushed to a size desirable for fiuidization, generally minus 14 mesh,and is fed into a first fluidized bed where it is maintained at atemperature sufiiciently below the fusion temperature of the coal toprevent the mass from fusing, but sufficiently high to removesubstantial quantities of volatiles in addition to unbound water. Inhigh volatile bituminous B coals, this range is from about 600 F. to 650F. Fluidization is by means of an inert gas, preferably hot flue gas,which both heats and fluidizes, although external heating may be used.About 1% to 10% of the weight of the dry coal is removed overhead duringa residence time of from about 1 to 30 minutes; of this overhead, abouthalf represents material conden'sable to oily hydrocarbon liquids.

The dried preheated coal is then fed into the second stage, in which thefirst pyrolysis occurs, where it is immediately heated to a highertemperature, but below its raised fusion point, to start driving off thebulk of the volatiles. The fiuidizing medium is, for the sake of heateconomy, the overhead from the third stage, and consists of gas pluscondensables from that stage. Residence time is from 1 to 30minutestemperature about 800 F. to 900 F. The second stage overheadincludes all the gas and condensables from the coal, excluding thatwhich came out of the drying-preheating stage. In general, there isenough condensable hydrocarbon to yield a total of about 24% to 25% oilyliquid by weight in the original dry coat. The amount of gas produced isa function of the way in which the fourth stage is operated, and can bevaried from about 10% to 30% by weight of the original coal. Residualchar (from the fourth stage) will vary from about 35% to 60% by weightof the original coal, reflecting both the treatment in the last stageand the ash level in the original coal. Alternatively, the fluidizingmedium may be any inert gas, and external heating may be used. But it isessential to avoid oxygen feed into this stage if high oil yields are tobe attained.

The partially devolatilized char from stage two goes into a third stagein which further fluidized bed pyrolysis is carried out, at temperaturesof the order of 950 F. to 1050 F. The fluidizing medium is preferablythe overhead from stage four. After 1 to 30 minutes in this stage, thechar contains little more than a percent or so of volatiles which arerecoverable as liquid condensates.

The char from stage three is fed into a fluidized calcination bedmaintained at a temperature between 1500 F. and 1800 F., by internalcombustion of the char by the gas fed into the reactor as a fiuidizingmedium, which may be air or oxygen. The overhead goes into stage threeto act as a fluidizing medium. It may contain a very small amount ofcondensables; otherwise its constituents are dependent on the amount ofoxygen in the fluidizing gas, and total residence time in the bed, thesetwo factors together controlling the temperature and the composition ofthe gas discharged. We prefer to operate at residence times of from 1 to30 minutes, and with high oxygen concentrations, to get about 1600 F. inthe bed, and an exit gas with high concentrations of hydrogen and carbonmonoxide.

Example 1 In order to determine what goes on in each of the individualstages, the process was operated with the stages independent of eachother, using nitrogen as the fluidizing medium, as an experimentalexpedient, in all the stages. The coal used was a high volatilebituminous B coal from the Illinois No. 6 Seam-Orient No. 3 Mine; on adry basis it contained 34.6% volatile matter, 58.8% fixed carbon and6.6% ash; ultimate analysis 74.9% carbon, 4.9% hydrogen, 1.8% nitrogen,1.1% sulfur, 10.7% oxygen, 6.6% ash. The fluidized bed reactor was anexternally heated stainless steel cylinder, 3 inches in diameter and 30inches high. Thirty pounds of coal were fed to stage 1, and theunderfiow from each stage was fed to the next stage, under theconditions indicated in the following table, to give the results thereindicated:

TABLE I.-FOURS'IAGE PYROLYSIS OF AN ILLINOIS NO.

6 SEAM COAL (ORIENT NO. 3 MINEl Stage 1 Stage 2 Stages Stage 3 StagesStage 4 Stages land2 lto3' 11:04

Operating Conditions:

Feed Rate, lb./hr 4. 3.0 3. 0 8.0 Fluidizing Gas Rate (N2),

t't./sec 0.6 0. 6 0.6 0 6 Avg. Bed Temperature, F. 600 850 l, 000 1,600Balances:

Overall 99 97 97 96 Carbon 103 98 105 99 Yields, wt. percent, dry basis:

Ch 83. 0 81.8 78. 6 64. 2 88.8 57.1 12.0 12. 9 11. 7 22. 5 1.8 23. 6 3.83.8 2.3 5.7 0.6 6.1 1.2 1.5 7.4 7.6 8.8 13.2 26. 7 28. 7 26. 0 50 4. O53 The experiment was repeated, using hydrogen as the fiuidizing gasthroughout; overall gas yield was about 8%, oil yield about the same asfor the run with nitrogen, char yield about 61%.

When the process is run continuously as shown in FIGURE 1, using hotflue gas, overhead from stage 3, overhead from stage 4, and oxygen asthe fluidizing gases, char yield is lowered to about 50%, oil yield isincreased to about 25% and gas yield is substantially increased.Moreover, the proportion of hydrogen in the gas is increased, so that itmay be used to react with the oil, in known fashion, to reduce itsviscosity, so that it is easier to pump.

High volatile A bituminous coal is much more susceptible to fusion, sothat five or six pyrolysis stages would be needed between the firstpreheating stage and the final calcination-gasification stage ifagglomeration were to be prevented. The necessary number of stages canbe reduced by blending the product from the first preheating stage withfrom 1 to 3 parts by weight of recycle char from a later stage ofpyrolysis. A typical flow sheet of such a process is shown in FIGURE 2.Oil yields are of the order of 25% to 32%; gas yields are from to 35%;and char yields are from 30% to 55%.

Example 2 A run was made as in FIGURE 2, using a high volatile Abituminous coa.lPittsburgh-Seam, Federal Mine. The coal was fed into the3 inch unit above described, at the rate of 4 pounds per hour, using 640F. in the first stage; 740 F. in the second stage, with 2 parts ofrecycle char from stage 4 added to 1 part of product from the firststage; 810 F. in the third stage, with an additional 1 part of char perpart of first stage product; 950 F..in the 4th stage; and 1600 F. in thefinal stage. The overall yield from the coal was Percent Char 45.6 Oil27.5 Aqueous liquor 7.0 Gas (CO free) 14.0 CO 5.9

In general, conditions can be varied as shown in the drawing, usingtemperatures from 600 F. to 650 F. in stage 1, 700 F. to 800 F. in stage2, 750 F. to 950 F. in stage 3, and 950 F. to lO50 F. in stage 4,depending on coal fed, rates of feed and other variables. Moreover, byadding more stages, less recycle is needed in the various pyrolysisStages.

Example 3 Char recycle can be used with Illinois No. 6 coal to reducethe total number of stages to three. Using the identical coal andapparatus used in Example 1 with nitrogen as the fluidizing means, coalwas fed to a first stage at 650 F., at a rate of 4 pounds per hour,until about 2.6% of volatiles were lost. This discharge was mixed heldfluidized with nitrogen, until a total of about 22% of the condensableoil had been removed; it was then fed to a calcination stage at 1600 F.,again fluidized with nitrogen, to recover the rest of the volatiles.Total yields were 54.7% char, 24.1% oil, 7.1% aqueous liquor, 11.2%combustible gas and 2.9% CO Ranges of yields for the various productsare essentially the same as for the conditions shown in FIGURE 1.

It should be noted that when recycle of char is used in our process, wedo not exceed a char to feed ratio of more than three to one. The use ofhigh ratios of recycle markedly reduces the throughput of the process,and sharply afiects the overall economy. The very low ratio of recycleis made possible by the pretreatment in stage one, where the verysignificant increase in fusion temperature is attained by the relativelyslight removal of condensable vapors overhead.

Obviously, changes can be made in the above examples, which can bemultiplied indefinitely, without departing from the scope of theinvention as defined in the claims. The invention is notonly applicableto high volatile bituminous A and B coals, where yields of 25% and moreof oils are obtainable, but it will increase the yields of oil fromother ranks of coal over known low pressure pyrolysis processes.

We claim:

1. In the process of pyrolyzing finely divided coal at low pressures inwhich the coal is heated in a plurality of fluidized beds atsuccessively higher temperatures to devolatilize the coal, the method ofincreasing the yield of oily liquids recoverable from the coal whichcomprises (1) in a first stage heating the finely divided coal below itsfusion temperature under oxygen-free conditions in a first fluidized bedformed by passing an inert gasiform stream upwardly through the stage tomaintain the coal in the fluidized state until about 1% to about 10% ofthe coal volatiles have been removed .r'as overheads and recovering oilyliquids from said overheads,

(2) in at least a second stage passing the so-treated coal into at leastone other fluidized bed which is fluidized by the gaseous overheads fromthe subsequent stages at a temperature above that of the first bed andbelow the fusion point of the solids fed to that stage, underoxygen-free conditions, for a time sufiicient to remove nearly all ofthe volatiles from the coal condensable to oily liquids,

(3) in a final stage passing the thus-treated coal into a finalfluidized bed which is fluidized by an oxygencontaining gas at a stillhigher temperature, to substantially devolatilize the coal, and

(4) recovering the oily liquids from all stages subsequent to the firststage from the overheads of the second stage.

2. The process of claim 1, in which one part of the treated coal fromthe first stage is introduced into the second stage, mixed with up tothree parts by weight of hot product from a stage beyond the secondstage.

3. In the process of pyrolyzing a high volatile bituminous B coal inwhich the finely divided coal is heated in a plurality of fluidized bedsat successively higher temperatures to devolatilize the coal, the methodof increasing the yield of oily liquids recoverable from the coal to therange of about 25% of the Weight of the dry coal, which comprises (1) ina first stage heating the coal to a temperature of about 600 F. to 650F. under oxygen-free conditions in a first fluidized bed formed bypassing an inert gasiform stream upwardly through the stage to maintainthe coal in the fluidized state until about 1% to about 10% of the coalvolatiles have been removed as overheads and recovering oily liquidsfrom said overheads.

(2) passing the thus-treated coal into a second fluidized bed which isfluidized by the gaseous overheads from the subsequent stages at atemperature of 800' F. to 850 F., under oxygen-free conditions for atime sufficient to remove substantial amounts of volatiles from theproduct,

(3) passing this partially pyrolyzed product into a third fluidized bedwhich is fluidized by the gaseous overheads from the subsequent stagesat a temperature of 950 F. to 1050" F., under oxygen-free conditions,for a time suflicient to reduce the remaining volatiles in the coalcondensable to oily liquids to no more than about 1%,

(4) passing this pyrolyzed product into a fourth fluidized bed which isfluidized by an oxygen-containing gas maintained at a temperature of1500 F. to 1600 F., to substantially devolatilize the char, and

(5) recovering the condensables from the overheads of all stagessubsequent to the first stage from the overheads of the second stage. i

4. The method of claim 3, in which oxygen containing gas is fed into thefourth fluidized bed to react with the char to provide heat, and theoverheads are fed counter" currently to the third and second stages toheat them.

5. In the process of pyrolyzing a high volatile bituminous B coal inwhich the finely divided coal is heated in a plurality of fluidized bedsat successively higher temperatures to devolatilize the coal, the methodof increasing the yield of oily liquids recoverable from the coal to therange of about 25% of the weight of the dry coal, which comprises (1) ina first stage, heating the coal to a temperature of about 600 F. to 650F. under oxygen-free conditions in a first fluidized bed formed bypassing an inert gasiform stream upwardly through the stage to maintainthe coal in the fluidized state until about 1% to about 10% of the coalvolatiles have been removed as overheads and recovering oily liquidsfrom said overheads,

(2) passing the thus-treated coal into a second fluidized bed of thetype aforesaid at a temperature of 900 F. to 1050 F., under oxygen-freeconditions, after mixing it with about twice its weight of recycle fromthe third stage for a time suflicient to reduce the volatilescondensable to oily liquids to no more than about 1%, of the originaldry coal,

(3) passing the pyrolyzed product into a third fluidized bed which isfluidized by an oxygen-containing gas maintained at a temperature of1500 F. to 1600 F. to substantially devolatilize the solids, and

(4) recovering the condensables from the overheads of all stagessubsequent to the first stage from the overheads of the second stage.

6. The method of claim 5 in which the third stage is fluidized with anoxygen containing gas containing at least as much oxygen as in air, andin which the second stage is fluidized by means of the overhead from thethird stage.

7. In the process of pyrolyzing a high volatile bituminous A coal inwhich the finely divided coal is heated in a plurality of fluidized bedsat successively higher temperatures to devolatilize the coal, the methodof increasing the yield of oily liquids recoverable from the coal to therange of about 25% to 32% of the weight of the dry coal, which comprises(1) in a first stage, heating the coal to a temperature of about 600 F.to 650 F. under oxygen-free conditions in a first fluidized bed formedby passing an inert gasiform stream upwardly through the stage tomaintain the coal in the fluidized state until about 1% to about 10% ofthe coal volatiles have been removed as overheads and recovering oilyliquids from said overheads,

(2) passing the thus treated coal after admixture therewith of 2 to 3parts by weight of product from one )of the further pyrolysis stagesinto a second fluidized bed of the type aforesaid at a temperature of700 F. to 800 F., for a time suflicient to remove substantial amounts ofvolatiles from the product,

(3) passing this partially pyrolyzed product into at least two morefluidized beds, of the type aforesaid, with a temperature in the latterfluidized bed of 950 F. to 1050 F. all under oxygen-free conditions, fora time sufficient to reduce the remaining volatiles condensable to oilyliquids to no more than about 1%, of the original dry coal,

(4) passing the pyrolyzed product into a final fluidized bed which isfluidized by an oxygen-containing gas maintained at a temperature of1500 F. to 1600 F., to substantially devolatilize the product, and

(5 recovering the condensables from the overheads of all stagessubsequent to the first stage from the overheads of the second stage.

8. The method of claim 7 in which the final fluidized bed is fluidizedwith an oxygen containing gas containing at least as much oxygen as air,and all the beds other than the first and the last are fluidized withthe overhead from the next succeeding bed.

References Cited UNITED STATES PATENTS 2,955,077 10/1960 Welinsky 201-313,047,472 7/1962 Gorin et al. 201-26 X 3,076,751 2/1963 Minet 201'MORRIS O. WOLK, Primary Examiner.

R. E. SERWIN, Assistant Examiner,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,375,175 March 26, 1968 Ralph Tracy Eddinger et a1.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Co1umn 3, line 6, "procesesd" should read processed COlUlIII'l 8, line31, after "800 F." insert under oxygen-free condltions Signed and sealedthis 30th day of September 1969.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

